1. Field of the Invention
The present invention relates generally to an electric motor driven switch machine for switching railroad tracks so that trains may switch from one track to another. More particularly, the present invention relates to a captive point detection system of a switch machine, for detecting, with a single switch position target, whether a railroad track has been properly switched, in order that such detection may indicated by indication means positioned locally at the switch machine or at a remote location.
2. Description of the Related Art
As is known in the art, a common method for switching a train from one railroad track to another is to install an electric motor driven switch machine next to a switching point of the track. Since modern versions of these switch machines are usually operated from a remote location, it is essential that a remote operator be able to determine that the switch has, in fact, been thrown as requested. Moreover, because switch point closure is imperative to safe railroad train operation, Federal Railroad Administration (FRA) rules and regulations mandate not only that the position of the switch points be mechanically locked to prevent the points from opening during train traffic, but also that the locked position of the switch points be continuously monitored to detect any undesirable movement. A circuit controller that includes a point detection system as an integral part of either a mainline switch machine or a stand-alone unit is used to accomplish this type of switch point monitoring, detection and subsequent indication to the switch machine or remote location.
A related art point detection and indication system is described by U.S. Pat. No. 5,669,587, issued Sep. 23, 1997 in the name of Van Alstine et al, which is hereby incorporated by reference in its entirety. In the Van Alstine et al. reference, there is provided an electric motor driven switch machine for positioning a railroad track at a switching point having rail point detection and indication mechanism. In particular, the detection and indication mechanism has a latch out mechanism that identifies a latch out condition when the railroad tracks are not at, or near, their proper positions before or after switching the railroad tracks. The detection and indication mechanism includes a four bar linkage which comprises a point detector bar, two cam followers, and a link arm assembly. The cam followers, supported in part by the link arm assembly, are connected to two point detector switches, so that the switch machine is operating when either one of these switches is closed or the railroad tracks are being switched.
Referring now to FIG. 1 herein, there is shown an overhead planar view of a typical related art point detection and indication system 100 housed within a portion of a switch machine 105, wherein a cover (not shown) of the switch machine 105 has been omitted from the figure. As is commonly known, the switch machine 105 is located adjacent to a set of stock rails having a set of switching rails situated therebetween (not shown). The general structure and positioning of switch machines relative to railroad tracks is known in the art and therefore, is not described in detail.
In the related art, a hand throw lever 110 (partially shown in phantom) is connected to a gear box (not shown) and is utilized typically for manual operation of the switch machine 105. Of the various components of the switch machine 105, only the base 115 of the switch machine 105 and the elements relevant to the operation of the related art detection and indication system 100 are shown. The basic design of the related art detection and indication system 100 typically includes a point detector bar 120 and adjacent normal and reverse cam followers 125, 130, respectively, which are generally each physically connected to mechanical linkages 135.
As is known in the art, the point detector bar 120 is a long cylindrical rod positioned perpendicular across the longitudinal axis of the switch machine 105 such that movement by the point detector bar 120 corresponds to movement by switching rails relative to the position of stock rail on either side (not shown). The point detector bar 120 typically passes through a wall 122 and a wall 124 of the switch machine 105. In FIG. 1, the wall 122 faces toward the railroad track (not shown) on a track side 140 and the wall 124 faces away from the railroad track on a field side 145. Typically, the point detector bar 120 is held in place with threaded adjustment bushings 150, 155, and a movable adjustment sleeve 160 that extends outwardly from the wall 122 and the wall 124 into the track side 140 and the field side 145, respectively. The point detector bar 120 is capable of moving in two opposing directions: a normal direction 165 and a reverse direction 170. When the point detector bar 120 is moving upward in FIG. 1 toward the railroad tracks (not shown) on the track side 140 of the switch machine 105, the bar is moving in the reverse direction 170; when the point detector bar 120 is moving downward in FIG. 1 toward the field side 145 of the switch machine 105, the bar is moving in the normal direction 165. Typically, a reverse cam 175 is defined at a fixed position on the point detector bar 120 and a normal cam 178 is defined by the movable adjustment sleeve 160 such that the detection and indication system 100 of the related art can identify movement by the switching rails by monitoring the position of the reverse cam 175 with the reverse cam follower 130 and the normal cam 178 with the normal cam follower 125.
A common problem in the related art electro-mechanical type point detection and indication systems is slack or lost motion in the mechanism that results due to wear over time. Related art point detection and indication systems of an electro-mechanical type typically detect the position of the point detector bar and related locking device using mechanical linkages to operate mechanical contacts, micro-switches, rotary switches, or a similar device. Over time, the mechanical linkages wear, thereby creating slack or lost motion in the mechanism. With undesired slack or lost motion, if the point detector bar should move unintentionally, thereby indicating unsafe switch point movement, the mechanical linkages detecting the internal point detector bar must move a given distance to take up or absorb the lost motion before the mechanical contacts or similar devices are actuated. The result is decreased sensitivity in switch point monitoring, which ultimately may cause an undesirable safety hazard.
Another problem with related art point detection and indication systems is that their design commonly requires the point detector bar to protrude out both sides of the switch machine. The protrusion of the point detector bar typically causes interference with the manual hand throw lever on dual controlled mechanisms. Interference between the hand throw lever and the protrusion of the internal point detector bar creates a pinch point 180 for a manual operator's hands, which is a safety hazard.
Another problem with related art point detection and indication systems is the complex manner that is required for adjusting a two-piece point detector bar that is connected to the switch machine and the track. As shown in FIG. 1, the two-piece point detector bar comprising point detector bar 120 and movable adjustment sleeve 160 typically passes through and is held in place by the bearings 150, 155. The point detector bar 120 is located on the track side 140 of the switch machine 105, and the movable adjustment sleeve 160 is located on the opposing track side 145 of the switch machine 105. The point detector bar 120 must be adjusted first at the fixed independent field side 140 of the switch machine, and then the movable adjustment sleeve 160 must be adjusted, thereby to align the cam followers 125, 130 and the mechanical linkages 135 to detect properly the normal cam 178 and the reverse cam 175, respectively. The complexity associated with adjusting the related art point detection systems requires a certain level of highly skilled and mechanically-inclined personnel to work on these devices. Maintaining a staff of highly skilled people is very costly to the railroads, and train operations typically become jeopardized by high personnel turnover rates and unavailability of personnel.
Consequently, a need exists for a point detection system that may be utilized with indication means, such as a related art circuit controller, for instance, wherein the point detection system minimizes the problems associated with: the slack or lost motion that results due to wear over time in the related art electro-mechanical type point detection systems; the point detection bar that protrudes from both sides of the switch machine; and the complex manner of adjusting related art two-piece point detection bars in a specified sequence.